Recently, a multi-antenna system has been attracting attention for achieving high frequency utilization efficiency in a limited frequency band. In order to implement the multi-antenna system, channel state information (CSI) may be required between a base station and a terminal.
Meanwhile, FIG. 8 is a view of an example of a multi-antenna system that obtains CSI by feeding back CSI from a user terminal (UT) to a base station (BS).
Referring to FIG. 8, the base station may include a multi-antenna 201 configured by N antennas 201-1 to 201-N, N transmitters Tx1 to TxN, and N receivers Rx1 to RxN respectively corresponding to the antennas 201-1 to 201-N. Furthermore, the base station may include N circulators 205-1 to 205-N and a controller 206 for respectively connecting transmitters Tx1 to TxN and receivers Rx1 to RxN to the antennas 201-1 to 201-N. Meanwhile, the terminal may include an antenna 101 and a control unit 107.
Referring to FIG. 8, in operation S23, the base station may start communication with the terminal through operation S21 of transmitting a signal for estimating CSI from the base station to the terminal and operation S22 of feeding back the signal for estimating CSI from the terminal to the base station. In addition, in the method of FIG. 8, CSI including information about a difference in amplitude and phase between a transmitter and a receiver may be estimated by feeding back the CSI. The number of times transmission and reception of signals for estimating CSI is performed increases depending on the number of antennas (the number of antenna elements) of the base station. Therefore, if the number of antennas of the base station or the number of users communicating with the base station increases, the amount of CSI feedback increases and communication efficiency may be greatly reduced.